Disc-shaped mixing tool with conically beveled through bones

ABSTRACT

A disc-shaped mixing tool (11) is used to mix liquids and to dissolve gases in liquids. The mixing tool (11) has a knife-sharp peripheral edge and several axial through bores (17), so that a liquid stream in the form of several cyclones (25) occurs upon rotation of the mixing tool (11). The bores (17) are each conically bevelled both on the upper and on the lower sides (13, 15) and are axially rounded off in the region (27) between the bevels in such a way that a radial airfoil profile (21) and, in a peripheral direction between adjacent bores (17), a peripheral airfoil profile (23) each result. Upon flowing through the bores (17) the liquid is spun radially outwards, resulting in tiny cavitation bubbles at the peripheral edge (19).

TECHNICAL FIELD

This invention refers to a disc-shaped mixing tool having an upper sideand a lower side, being rotatable around a central axis and havingseveral axial through bores, with at least one of the two sides of thedisc being convex.

BACKGROUND ART

A mixing tool of this kind is already known from U.S. Pat. No.4,007,920, FIG. 18. This known mixing tool is in the shape of a disc, isrotatable around a central axis, and is provided with several axialthrough bores, with one of the two sides of the disc being convex. Thethrough bores serve to introduce air adjacent to the upper side of themixing tool into a liquid adjacent to the lower side of the mixing tool.The mixing effect of this known tool, however, is in need ofimprovement, since for a thorough mixing of liquid and gas the knownmixing tool must rotate for a relatively long time and a large amount ofenergy is therefore consumed.

Another mixing tool of the type given above is the subject matter of twoolder, not prepublished proposals of the applicant (EP 0 495 506 A2 andDE 41 13 578 A1). The mixing tool therein is designed as a discus-likedisc and has different curvatures on its upper and lower sides. The discitself is caused to rotate by a drive, so that a pressure differencebetween the upper and lower sides arises as a result of the Bernoullieffect. As the disc has several axial bores, an axial stream created bythe pressure difference occurs between the upper and lower sides. Thestream flows through the axial bores, so that an intensive blending ofseveral fluids can take place as a result of the flow from the lowerside to the upper side. In addition, the known disc is provided with aknife-sharp peripheral edge to prevent a flow around the disc. At arotary speed of 3000 to 8000 revolutions per minute and a disc diameterof 42 mm the stream is so strong that cavitation occurs at theperipheral edge of the disc and even gases can be dispersed into thetiniest bubbles and dissolved in fluids, whereby the finest foams,suspensions and emulsions are produced.

Cavitation appearances also occur, for instance, with turbine blades orship propellers. If a liquid is caused to flow at a high speed, cavitieswith strong partial vacuums are formed in the liquid. When thesecavities implode, pressure thrusts are released, which can cause damageto turbine blades and ship propellers in the form of cavitation erosionor cavitation corrosion.

To be sure, the discs according to the above two older proposals of theapplicant have proved themselves in practical application; however,endeavours are being made to further increase their cavitation effect,in order to render the mixing of liquids and/or gases even more rapidand even more thorough.

DISCLOSURE OF INVENTION

The object of the invention is to provide an improved mixing tool formore rapid and more thorough mixture of liquids and/or gases.

In the mixing tool according to the invention, the bores are eachconically bevelled at the upper and at the lower side of the mixing tooland the peripheral edge is knife-sharp, so that wing-like profiles areformed. On the one hand, an airfoil profile is thus created in a radialdirection between the bores and the knife-sharp peripheral edge; on theother hand, an additional airfoil profile is created in a peripheraldirection each between adjacent bores. The result of this is that whenthe rotating mixing tool is immersed in a fluid or in several fluids tobe mixed, cyclones develop. A partial vacuum develops at the upper sideof the mixing tool, whereby liquid present at the lower side issubjected to a suction effect. One cyclone of fluid per bore develops inthe region of the bore on the lower side of the mixing tool. Adhesionforces on the upper side of the mixing tool, combined with a highcentrifugal force, cause the fluid to be radially spun away upon flowingthrough the bores. Cavitation takes place in the range of high shearingforces, predominantly at the knife-sharp peripheral edge. A defineddirection of flow is formed by the airfoil profiles in the radial andperipheral directions on the basis of the pressure differences betweenthe upper and lower sides. Moreover, the flow through the bores and thesubsequent flow around the upper side of the mixing tool in a radialdirection are substantially improved, whereby the suction effect isincreased, flow losses are avoided and, thanks to a thereby increasedradial flow rate, the cavitation effect and the mixing effect areimproved.

BRIEF DESCRIPTION OF DRAWINGS

One embodiment according to the invention is described in greater detailbelow, with reference to the drawings.

FIG. 1 shows a cross section through an embodiment of the mixing toolaccording to the invention and two cyclones,

FIG. 2 shows a bottom view of the mixing tool according to FIG. 1,

FIG. 3 shows a sectional view of the mixing tool along line 3--3 in FIG.2, and

FIG. 4 shows a cross section of another embodiment of the mixing toolaccording to the invention.

BEST MODE OF CARRYING OUT THE INVENTION

FIG. 1 shows a mixing tool 11 with an upper side 13 and a lower side 15.On the upper side 13 an axially protruding flange F extends centricallywith reference to a central axis Z of the mixing tool 11 and has acentric bore 30 via which the mixing tool 11 is coupled to a drive R andcan be put into rotation. The mixing tool 11 has a knife-sharpperipheral edge 19 and four axial through bores 17.

The bores 17 are conically bevelled both on the upper and the lowersides 13, 15, for example by a specially designed countersinker with itstip directed towards the central axis Z of the mixing tool 11. Inaddition, in the areas 27, 27' axially between the bevels, the bores 17are each rounded off in such a way that the nose of an airfoil profile21 is formed in a radial direction between the bores 17 and theknife-sharp peripheral edge 19.

The mixing tool 11 has a flat, curved profile on its upper and lowersides 13, 15. The lower side 15 preferably has a more flatly curvedprofile than the upper side 13, so that the airfoil profile 21 isadapted to an aeroplane wing profile in a radial direction, and thus--asin the lift exerted on an aeroplane wing--a suction effect described ingreater detail below occurs, this suction effect being substantiallystronger than if the upper and lower sides had been equally curved.

FIG. 2 shows the bores 17 evenly distributed around the periphery of themixing tool 11 on a circle concentric to the same and each having thesame diameter. In addition, however, it is also conceivable for bores 17of different sizes to be distributed on several concentric circles ofthe mixing tool 11.

FIG. 3 shows a cut along line 3--3 in FIG. 2 through two adjacent bores17. Here it can be seen that between the bores 17 in a peripheraldirection an airfoil profile 23 is likewise created; it does not have acompletely ideal airfoil profile cross section, as the airfoil profile23 does not taper to a point in a radial direction as does the airfoilprofile 21, but rather has radii in the area 27' axially between thebevels. The conical bevels of the bores 17 on the upper and lower sides13, 15 each lie on the surface area of an imaginary frustum with itsline of symmetry outwardly inclined away from the central axis Z of themixing tool 11. In the production of the countersinks by acountersinking tool, this geometry results from placing thecountersinking tool relatively at right angles to the upper and lowersides 13, 15, respectively, which, in the mixing tool 11 with a convexprofile, means that the countersinking tool is placed at such a slantthat its tip is pointed towards the central axis Z.

Furthermore, it is possible according to FIG. 4 to concavely curve theupper side 13 axially towards the inside and to convexly curve the lowerside 15 axially towards the outside between the central axis Z and theperipheral edge 19. In this case as well, together with the countersinksa wing profile results both in the radial and the peripheral directions.

To be sure, the flange F is advantageous, but it can be omittedaltogether and the drive R can be connected by other common couplingelements.

The terms upper and lower sides used here are interchangeable. Thatwould only influence the direction of flow.

The mode of operation of the mixing tool is explained in more detailbelow on the basis of FIG. 1.

Merely the lower side of the mixing tool 11 is dipped into a not showncontainer filled, for example, with water and oil, so that the upperside 13 is not wet. The drive R drives the mixing tool 11 so that itrotates, for instance, at approximately 6000 revolutions per minute.

In conventional mixers such as those in the shape of a beater, themixing is produced by protruding edges which sweep the liquid along. Ina beater, which has a twisted screw-like shape, the liquid to be mixedis additionally transported towards the surface of the fluid by adeveloping conveying effect and, moreover, is spun outwards by thecentrifugal force and the protruding edges, whereby the desired mixingtakes place.

To be sure, the disc-shaped mixing tool 11 acts like a stirrer, butworks in accordance with a different principle. On rotation of themixing tool 11 a pressure difference between the upper and lower sides13, 15 develops due to the Bernoulli effect. A resultant partial vacuumat the upper side 13 causes the fluid at the lower side 15 to be drawnin. The suction effect in this is so great that several cyclones 25,similar to whirlwinds, come into being. The number of cyclones 25corresponds to the number of bores 17 in the mixing tool 11. Thediameter of the cyclones 25 is also approximately equal to that of thebores. The fluid thus put in motion flows upwardly at a high rate andflows through the axial bores 17. Due to the adhesion of the liquid tothe upper side 13, the fluid is subjected to an additional centrifugalforce and is spun radially outwards. Thus the turbulent stream in theregion of the cyclones 25 is laminarly aligned upon flowing through thebores 17, resulting in an increased rate of flow on the upper side 13and, consequently, a higher differential pressure between the upper side13 and the lower side 15.

The appearing streamline of individual fluid particles is not preciselyradial with reference to the mixing tool 11. The superposition ofperipheral speed and radial speed results in an arc-shaped flow path ofthe fluid particles and hence of the fluid in the direction of theperipheral edge 19 of the mixing tool 11. In this the flow around theupper side 13 is smooth and laminar, without major additional turbulenceand flow losses, similar to the wing of an aeroplane.

Fluid particles which have flowed through the bores 17 can reach theupper side 13 and be spun outwards not only in the region of the bores17 which is located near the peripheral edge 19 of the mixing tool 11;it is also equally possible for fluid particles to reach the upper side13 in the region of the bores 17 which is near the central axis Z. Indoing so these fluid particles, as already explained, describe anarc-shaped path towards the peripheral edge 19. On the arc-shaped pathas well a stream results, flowing along an airfoil profile representinga combination of the airfoil profile 21 in a radial direction and theairfoil profile 23 in a peripheral direction. This developing airfoilprofile has a nose corresponding to the airfoil profile 23 with arelatively large radius in the area 27' between the countersinks and hasa rear edge formed by the peripheral edge 19. The airfoil profile 23 isthus not completely engulfed by the flow, but rather forms the nose ofthe developing airfoil profile, depending on the arc-shaped pathdescribed by the fluid particles. This in turn depends on the geometryof the mixing tool 11, its rotational speed and the type of fluids to bemixed.

In the region of high rates of flow, particularly in the region of theperipheral edge 19, high shearing forces within the fluids to be mixedresult in the formation of tiny cavitation bubbles, i.e. low-pressurecavities. Cavitation is mechanically produced.

The fluids to be mixed are mixed substantially more rapidly andthoroughly than with conventional stirring means not only through thehigh rates of flow, but also through the cavitation itself. The tinycavitation bubbles implode again upon their formation, whereby strongpressure thrusts occur, creating an additional mixing effect. If onlythe lower side of the mixing tool 11 is dipped into the fluid or thefluids to be mixed, air or gas, if such is present at the fluid surface,is also drawn in. The gas in this is so completely mixed that it ispartially dissolved in the mixed fluid. This is explained by the factthat the air penetrates into the tiny cavitation bubbles developing andfills out the cavities thus formed.

Whereas due to the radially outward flow no more fluid at all is presentin the region of the flange F when the mixing tool 11 is rotating, anadditional stream 33 appears on the lower side 15 in the area of thecentral axis Z, between the cyclones 25. This stream 33 also developsdue to the strong partial vacuum between the upper and lower sides 13,15. The stream 33 passes near the lower side 15 radially towards theoutside and is partially deflected by the cyclones 25 and/or flowsradially on the lower side 15 to the peripheral edge 19.

The upper and lower sides 13, 15 have a flat, convexly outwardly curvedprofile, with a very wide variety of profiles--as in the case ofaeroplane wing profiles--as well as different bevels being conceivable.Depending on the type of bevel and profile, a different airfoil profile21 and/or airfoil profile 23 results. As in an aeroplane wing, however,it is advantageous to provide the lower side 15 with a more flatlycurved profile than the upper side 13, whereby in the cavitation disc11, comparable to the lift effect on an aeroplane wing, an increase inthe pressure difference occurs, resulting in an increase in the suctioneffect arising.

The ratio of the curvature of the upper side 13 to that of the lowerside 15 is defined by a ratio of their surface lines. The surface lineof the upper and the lower side 13, 15, respectively, passes in thisconnection through the central axis Z of the mixing tool 11 and connectstwo diametrically opposed points of the peripheral edge 19, with theflange F being disregarded in this. Mixing tools 11 with a length ratioof upper surface line to lower surface line of from 1.15 to 1.75 haveproved to be particularly advantageous, wherein as the nominalrotational speed at which the mixing tool 11 works increases, the ratioof the lengths of the surface lines also advantageously rises.

Prototypes of the mixing tool 11 with diameters of up to 300 mm haveshown that with the mixing tool 11 it is possible to completely mixfluids within an extremely short time.

The suction effect occurring in this is so great that it also appears tobe conceivable to use the mixing tool 11 as a drive element similar to arotor or a ship propeller.

Disc-shaped mixing tools 11 with a large length ratio of upper surfaceline to lower surface line, i.e. with a heavily curved upper side 13 anda more flatly curved lower side 15, can also be used to separate fluidsor to eliminate particles from fluids. For instance, it is possible toseparate a mixture of oil and water using the mixing tool 11. In doingso, the different densities of the fluids are exploited, since,depending on their density, the fluid particles on the upper side 13 arespun different distances towards the outside, and a correspondinglylonger or shorter flight path results.

In one form in which the mixing tool 11 is made of nickel, the tooladditionally has a catalytic effect in the production of an oil-watermixture or a petrol-water mixture. The nickel here acts in each case asa catalyst for the separation of hydrogen from the water and thus forthe formation of radical OH groups.

I claim:
 1. A disc-shaped mixing tool (11) having an upper side (13) anda lower side (15), being rotatable around a central axis (Z) and havingseveral axial through bores (17), with at least one of the two sides(13, 15) of the disc being convex, characterized in that the peripheraledge (19) of the disc is knife-sharp, and wherein each bore (17) has anupper side (13) and a lower side (15), each bore (17) being conicallybevelled to form bevels at the upper side (13) and at the lower sidethereof (15), so that airfoil profiles are formed between the bores (17)and the peripheral edge (19) in a radial direction and between adjacentbores (17) in a peripheral direction.
 2. A mixing tool (11) according toclaim 1, wherein a region is defined between the bevels, and wherein thebores (17) are each rounded off axially in the region (27, 27') betweenthe bevels.
 3. A mixing tool according to claim 1, characterized in thatthe bores (17) are uniformly distributed on a concentric circle of thedisc.
 4. A mixing tool according to claim 1, characterized in that thebores (17) each have the same diameter.
 5. A mixing tool according toclaim 1, characterized in that the upper and lower sides (13, 15) of thedisk each have a flat, convex profile curved axially outwards.
 6. Amixing tool according to claim 1, wherein the upper and lower sides (13,15) each have a curved profile, and wherein the lower side (15) of thedisk has a more flatly curved profile than the upper side (13).
 7. Amixing tool according to claim 1, characterized in that the upper side(13) of the disk has a concave profile curved axially inwards betweenthe central axis (Z) and the peripheral edge (19), and that the lowerside (15) of the disk has a convex profile curved axially outwards.
 8. Amixing tool according to claim 1, wherein a first surface line whichpasses on the upper side (13) of the disk through the central axis (Z)of the disc and extends between diametrically opposed points on theperipheral edge (19) has a first length, and a corresponding surfaceline which passes on the lower side (15) of the disk has a secondlength, and the length of the first surface line is 1.15 to 1.75 timesthe length of the corresponding surface line of the lower side (15). 9.A mixing tool according to claim 1, characterized in that the conicalbevels of the bores (17) on the upper and lower sides (13, 15) thereofeach lie on the surface area of an imaginary frustum, with the axis ofsymmetry thereof being inclined in a direction opposite from the disc,outwardly away from the central axis (Z) of the disc.
 10. A mixing toolaccording to claim 1, characterized in that the disk consists of nickel.